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Tropical Storm HENRI (Text)


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Tropical Storm Henri Discussion Number  16
NWS National Hurricane Center Miami FL       AL082021
500 PM EDT Thu Aug 19 2021
 
The Air Force Hurricane Hunters investigated Henri earlier this
afternoon and found maximum flight-level winds and SFMR values to
support an intensity of about 55 kt and a minimum pressure of 997
mb.  The storm's appearance in satellite images has been generally
steady throughout the day with the low-level center located on the
northern side of the convective mass, and banding features confined
to the south side of the circulation.  This somewhat asymmetric
cloud pattern is due to about 25 kt of north-northeasterly shear.
 
The tropical storm is now moving due westward at 9 kt.  A mid-level
ridge should keep Henri on a westward to west-northwestward track
through tonight.  On Friday, however, a trough is expected to cut
off over the Ohio Valley and mid-Atlantic region of the U.S. while a
ridge amplifies to the east of Henri over the western Atlantic.  A
combination of these features should cause Henri to turn northward
on Friday and accelerate in that direction over the weekend.  The
exact location of the northward turn will be very critical in
determining Henri's future track and how close it gets to New
England.  The latest GFS run has shifted eastward and the UKMET and
ECMWF have shifted westward. Consequently, the net result is very
little change in the consensus models and the new NHC track
forecast is just a little faster than the previous one.  Based on
this forecast, Henri is expected to be very near southern New
England on Sunday and Monday. The NOAA Gulfstream IV jet will be
flying around Henri this evening to help assess the environmental
conditions and gather data for the numerical models. It is hoped
that these data will help the models more accurately predict the
future track of the storm.
 
Although Henri is a bit weaker now, the overall intensity forecast
philosophy has not changed.  The shear is expected to persist for
another 12 to 24 hours, so little change in strength seems likely
during that time period.  However, the global models show a more
conducive upper-level wind pattern over Henri shortly after that,
and in fact, all of the environmental conditions appear favorable
for strengthening on Friday and Saturday.  Therefore, steady
intensification is expected during the 24-60 h time period, and
Henri is forecast to become a hurricane during that time.  Henri is
expected to cross the north wall of the Gulf Stream and move over
much cooler SSTs on Sunday, and that should end the opportunity for
strengthening and induce a steady weakening trend from days 3 to 5.
Post-tropical transition is now shown to occur by the end of the
forecast period when Henri is expected to be over SSTs below 20
deg C.
 
It should be noted that as Henri gains latitude and moves near
New England, the wind field is expected to expand.  Therefore,
users are reminded to not focus on the exact forecast points as
impacts will extend far from the center.
 
Key Messages:
 
1. Henri is forecast to be near the northeast coast of the U.S.
on Sunday and Monday, and the risks of storm surge, wind, and rain
impacts in portions of southern New England and eastern Long Island
are increasing.  Watches will likely be required for portions of
this area early Friday.
 
2. Swells from Henri will begin to reach much of the east coast of
the U.S. and Atlantic Canada by the end of the week and continue
through the weekend. These swells could cause life-threatening surf
and rip currents.
 
3. Heavy rainfall may lead to flash, urban, and small stream
flooding over portions of southeastern New England Sunday into
Monday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  19/2100Z 29.7N  71.4W   55 KT  65 MPH
 12H  20/0600Z 30.1N  72.6W   55 KT  65 MPH
 24H  20/1800Z 31.0N  73.2W   55 KT  65 MPH
 36H  21/0600Z 33.0N  72.6W   65 KT  75 MPH
 48H  21/1800Z 36.0N  71.3W   75 KT  85 MPH
 60H  22/0600Z 38.9N  70.3W   80 KT  90 MPH
 72H  22/1800Z 40.8N  70.1W   65 KT  75 MPH
 96H  23/1800Z 42.3N  69.6W   50 KT  60 MPH
120H  24/1800Z 43.6N  65.7W   40 KT  45 MPH...POST-TROPICAL
 
$$
Forecaster Cangialosi
 
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Page last modified: Monday, 06-Dec-2021 12:09:17 UTC